Continuity mistake: Rambo plays a game where you have to pick up a dead sheep and throw it into a circle. He reaches down from his horse to pick up a huge, black, fake and dry sheep with his right arm. The next scene shows him with a small, wet, real dead sheep but now it's in his left hand.
Continuity mistake: When Rambo goes through the mine field his knife changes. Sometimes it has saw teeth(like the one in First Blood) and sometimes not. You'll see it when he finds the mine. Stallone wasn't satisfied with master knife maker Gil Hibben's first model for the movie and the knife was changed after the mine field scene was shot and some close ups of the new Rambo knife were made later on.